Use a comma between consecutive coordinate adjectives. Don’t use a comma between cumulative adjectives.
Coordinate adjectives modify a noun equally and separately:
Literature students favor long, difficult, page-turning books.
When coordinate, each adjective modifies the same noun separately and equally. The word “and” could join each adjective. They also make sense if rearranged.
Literature students favor page-turning, difficult, long books.
Literature students favor page-turning, long, difficult books.
It was a playful, colorful noise.
It was a colorful, playful noise.
She smiled at the thought of the desperate, dark acts ahead.
She smiled at the thought of the dark, desperate acts ahead.
Some adjectives are cumulative and should not be separated with commas.
Janey smelled the earthy Brazilian coffee.
She then plunged fork into sweet cherry pie.
Did you see the five small brown rats taking a swim?
The room had that pungent old book smell.
not: The room had that pungent book old smell.
possibly: The room had that old pungent book smell.
The modification power of cumulative adjectives is suggested by their name. One adjective modifies a noun, a second (or third) adjective modifies the other adjective(s) as well as the noun.
Worksheet for using Commas with adjectives